Method of manufacturing selenium rectifiers



Jan. 28, 1941. G. HOPPE Em. 2,229,807

METHOD OF MANUFACTURING SELENIUM RECTIFIERS Filed May 51, 1939 Patented Jan. 1941 RECTIFIERS Georg Hoppe, Berlin, and Heinrich Schliigel, Berlin-Hermsdorf, Germany, assignors to Patentverwertungs Gescllschaft mit beschriinkter Haftnng Hermes, Berlin, Germany, a corporation of Germany Application May 31, 1939, Serial No. 276,646

Germany May 7, 1938 4 Claims.

This invention relates to a method of menufacturing selenium rectifiers.

Dry rectifiers for small currents require elecf trode disks of a correspondingly small diameter. 5 If, however, the diameter is smaller than 1 cm.,

for instance only some millimeters, the manufacture and assembly of the rectifiers is complicated and time absorbing owing to the small size of the disks. It is particularly diflicult .to apply to disks of such a small size a selenium coating in a sumciently uniform manner and to limit the coating to only one side of the disks.

It is an object of the present invention to eliminate these difiiculties and to facilitate and improve the manufacture of such selenium-rectifiers. According to the invention a support of sheet metal is first provided with a uniform coating of selenium, and disks of the desired small dimensions are then punched out from the larger ones. The punching operation is effected after a layer of molten selenium has been applied to the support and cooled down, but before the selenium has been rendered conductive by a heat treatment. It has been found that the layer of selenium has often the tendency to scale and therefore cannot always withstand the strain when punching the disk. However, before rendering the layer of selenium conductive it is considerably more tenacious and adheres to the support in such amanner that it is not appreciably damaged during the punching operation. It scales at most in the immediate neighborhood of the point where the disk is punched, at which point the layer, as a rule, need not be conductive.

The application of the molten selenium to the larger support is considerably simpler and may also be effected in a more uniform manner than in the case of a disk having a'diameter of only a few millimeters. Experience has shown that such small rectifier disks, if manufactured by the stamping process before the selenium layer has become conductive, have a higher average stopphase voltage than that obtainable when applying the molten selenium to the individual small disks. 5 This is probably due to the greater uniformity of the selenium coating applied to the largeqsupport.

The application of the layer of molten selenium to larger metal supports, if effected by a mechan- 50 ical method or by hand, is so advantageous that the invention is also useful when manufacturing rectifier disks of relatively large size because of I the more economical manufacture and, in many cases, because of the improved quality of the rec- 55 tifiers produced according to the invention.

The drawing serves to further elucidate the method according to the invention. and shows in Fig. 1 a circular metal sheet and its division into a multitude of rectifier disks as obtained by stamping operations, in

Fig. 2 a metal strip out of which rectifier disks are to be punched, and in Fig. 3 another strip divided into rectifier plates of square shape.

Fig. 1 shows an aluminum disk I, for instance. of a diameter of 100 mm. which isfreed of oxide and roughened by means of a jet sand blast.

Molten selenium is applied to the disk I, cooled down and solidified preferably under a press, after which the disks 2 are punched out from the disk l.- In the embodiment shown, the disks 2 have a diameter of about 20 mm. The disks 2 may be' ered as waste, but may also be employed in the manufacture of other rectifiers, since disks of such small diameters, for instance, of 3, 5 or 7 mm., are often necessary. Also those portions of the disk I which are left after punching out the disks 2 may be used for stamping out very small rectifier disks 9, so that the material coated with selenium is utilized to the greatest possible extent. This method reduces not only waste material, but also the number of rejects which in the known methods are due to the fact that part of the selenium reaches the back side of the disks and causes a short circuit.

The portions 2, 3 and 9 punched out from the disk I are then exposed in a furnace for one or more hours to a temperature of about 200 degrees centigrade, and the furnace is left open during this period to such an extent as to permit the entrance of air from outside. After the selenium coating has cooled down to room temperature it is exposed for a short time ,to the action of sulphur vapors. In this manner a continuous layer of sulphur is produced on the selenium coating;

on which layer is sprayed a layer of a metal or alloy of low fusibility. Good results may be obtained with an alloy of cadmium and bismuth. The alloy to be sprayed on a layer must be made of pure constituents and be protected against impurities if high-grade rectifiers are to be manufactured. v

or, polarized by the action of an electric current, in particular by applying a direct voltage in the direction of the stop phase. This current causes heating and polarizing o! the disks until the initial current is reduced to a few milliamperea;

iler disks 2 as well as the rectifier disks 3 and 9 become ready for operation.

According to the embodimentof the invention shown in Fig. 2, the selenium coating is applied to a metal strip 4. When the layer is solidified the disks i are punched out and treated in the manner described above. When producing disks.

on a large scale, a band in motion is particulirly suitable for applying the selenium coating. 'Ihis band may be advanced intermittently and while the selenium coating applied to one portion of the band cools down under the press, the next portion of the band is provided with the layer of selenium. The band may, however, be moved continuously if the pressis so arranged that it advances with the cooled-down portion and then returns each time to the initial point. Oi course, very small rectifier disks 6 of the desired size may be stamped out oi! the disks 5 as shown in Fig. 2 and from the remaining por-- tion of the band further small disks 9 may be punched out.

In a particularly simple manner, square rectiiler plates may be cut oil from a band in motion as apparent from Fig. 3. In this case the band I is cutinto individual rectifier elements 8. The latter may also be provided with a perforation in order to enable a threading of the elements on a bolt.

In the above forms 0! theinvention it is assumed that the selenium coating is applied to an aluminium support. The method according to theinvention may also be used in the manufactuiie of selenium rectifiers in which the selenium o is'ipplied to sheet metal of the iron group or of The rectifier disks thus treated are then formed copper or the alloys-thereof, or to a substratum of graphite or the like.

What is claimed is:

l. The method oi! manufacturing electrode disks for dry rectiflers having a metallic suport covered with a selenium coating, which comprises the steps of providing a plain metal sheet with a coating of selenium in its non-conductive modification, punching said disks from said coated sheet and completely separating said disks, and heat-treating said disks to convert said selenium into its conductive modification.

2. The method of manufacturing electrode disks for dry rectiilers having a metallic support covered with a selenium coating, which comprises the steps of providing an extensive metallic support with a coating of molten se1enium,al1owing said coating to cool, punching rectifier disks of different diameters from said support, a disk 01' small diameter being punched out o! the centers of large disks respectively in order to permit threading a number of said large disks on a bolt,

and heat-treating said ditierent disks so as to render said selenium coating conductive.

3. The method of manufacturing electrode disks for dry rectifiers having a metallic support covered with a selenium coating, which comprises the steps of providing a metal strip with a molten selenium coating, punching said disks out of said strip, said coating step and said punching step being eiiected in one continuous operation yet at spaced locations, and feeding said strip from the location of said coating step to that of said punchi'ng step so as to cause said coating to cool down between said steps. a 4. The method of manufacturing electrode disks for dry rectifiers having a metallic support covered with a selenium coating, which comprises the steps of punching said disks from an aluminum strip, and coating said strip with selenium previous to the punching and while feeding said strip to the punching operation.

/, GEORG HOPPE.

HEINRICH scHLiiGEL. 

